During manufacture of a glass container, defects may be introduced into one or more sidewalls of the glass container. An exemplary defect in glass containers is insufficient sidewall thickness. A glass container with insufficient sidewall thickness may be at risk to break when it is populated with content, especially when the content is a liquid that is sprayed into the glass container at a high velocity.
When a glass container breaks due to insufficient sidewall thickness, a production and/or filling line may be required to be shut down while the broken glass container is cleaned up, thus leading to decreased glass container production and/or filling. There are several approaches for testing glass containers for insufficient sidewall thickness. A first exemplary approach uses a capacitive sensor system. In this approach, electrodes are placed in physical contact with the exterior of the sidewall of the container, and a value that is indicative of capacitance of a region of the glass corresponding to where the electrodes are in contact with the exterior of the sidewall is obtained. The value can be used to derive a thickness of the sidewall at the region of the glass. The container can then be rotated while the electrodes remain in contact with the sidewall of the container, such that thickness of the glass container can be ascertained for a cross-section of the container. This approach is not practical for testing the thickness of the entirety of the glass container, as the measurement only tests the thickness through a plane that extends through the glass container. Additionally, this approach requires physical contact of the electrodes with the glass container and rotation of the glass container, which is disadvantageous as it may interfere with glass container production and/or filling.
A second exemplary conventional approach utilizes a laser. The laser is configured to emit a laser beam at an acute angle relative to the exterior of the sidewall of the glass container. When the laser beam reaches the sidewall, part of the laser beam reflects off the exterior surface of the sidewall and another part of the laser beam reflects off the interior surface of the sidewall. An optical sensor captures these two reflections, and a distance between the captured reflections can be used to determine thickness of the sidewall at the point on the sidewall where the laser impinges upon the sidewall. While this approach does not require physical contact (such as in the first approach), it can only test sidewall thickness at specific points along the sidewalls of the glass container. Like the approach described above, the number of points on the sidewalls of the glass container for which thickness values can be obtained can be increased by rotating the container while the laser beam is directed towards the container. Requiring that the glass container be rotated to inspect thickness may interfere with production and filling of glass containers.
Another exemplary conventional approach for determining thickness at points along a sidewall of glass container includes the use of a chromatic confocal sensor to ascertain thickness at individual points along the sidewall; this approach has deficiencies similar to the deficiencies of the approaches described above, in that measurements are limited to single points, and to acquire additional measurements involves rotating the glass container. Moreover, for each of the approaches referenced above, the sensors must either be in close proximity to or in contact with the sidewall of the glass container while the glass container is being rotated; accordingly, the conventional approaches referenced above are limited to measuring thickness of cylindrical glass containers, and are ill-suited for measuring thickness of non-round glass containers.
Yet another conventional approach utilizes a short-wavelength infrared camera (i.e., a camera configured to detect radiation having wavelengths between 1.4-3 μm). After a glass container has been produced and while the glass container is still hot, the container is placed in a brick oven. Responsive to the glass container being uniformly heated, the glass container will radiate energy. The thicker the sidewall of the glass container, the more energy that will be radiated from the sidewall. The infrared camera captures an image of short-wavelength infrared radiation being irradiated from the container. A thickness of a point on the sidewall captured in the image is ascertained utilizing any suitable approach, and a thickness distribution over a region of the sidewall of the glass container is computed based upon intensity values of the image and the ascertained thickness at the point on the sidewall. While this approach can test sidewall thickness along a region of the sidewall (unlike the approaches described above), it requires that the glass container be heated to a high temperature in order for the camera to be able to capture short-wavelength infrared radiation being radiated from the glass container. Additionally, glass is transparent to short-wavelength infrared radiation. Thus, the image generated by the camera may include unwanted artifacts in the form of infrared radiation being irradiated from an opposite side of the glass container, which can lead to an incorrect thickness assessment.